# starship-design: Genuine STR question

```Greetings,

I want to make sure my naive conception of
special relativity is hunkey-dory with a more
intensive understanding, with regard to reaction
mass.

Your ship has a comfortable supply of reaction
mass, and adequate energy reserves. You determine
your reaction mass will be optimally used if it is
fully ionized, and accelerated into the relativistic
realm of velocities with a linear accelerator you
have handy on board. ( The electrons are no
problem, for they are boosted to relativistic
velocities quite easily with electrostatics. )

In the coordinate frame of the ship, still dawdling
within the Newtonian velocity space, your linac
is boosting the particles which comprise your
reaction mass into the relativistic velocity realm.
These particles approach the asymptotic limit C;
as they do, the energy increment you must supply
to produce further acceleration grows exponentially.

Your labor is not unrewarded, for the "extra" energy
( departure from linear Newtonian term ) you have
placed into accelerating these stubborn particles,
shows up as an increase of their mass. Your inertial
transfer is a function of their new equivalent mass,
not of their rest mass. In short, your overall reaction
engine is boosted by the multiplier amounting to the
relativistic increase in mass you impart to your ejecta.

The net effect of this consideration, is to reduce the
amount of reaction mass required for a given acceleration.
( Strictly, you traded it for energy, but we can assume
ample energy, for the intro paragraph says so! ) The
big worry is whether enough reaction mass is available,
which is in short supply in fairly empty space. There are
tricks to come up with energy, it's fairly portable
compared to fuel.

Do you feel this logic holds, with respect to the inertial
exchange of the reaction engine receiving the benefits of
the relativistic mass boost? Conservation is preserved on
the mass-energy product, which makes it seem likely to
me. Is not the corollary, that a relativistic jet becomes an
optimization of the reaction engine, and for really fast
ships we should be thinking in terms of high flux particle
accelerators in every case, to reduce the amount of
reaction mass required for the jet in Newtonian mode?

Just trying to clear my thoughts on this topic.

Cheers,
Johnny Thunderbird
http://www.geocities.com/~jthunderbird/drive.html
```